If the HIC valve is open when the Curb Idle is set, THEN when the HIC Valve is closed and the Fast Idle Cam is off, the Curb Idle of the engine may be too low and the engine may stall.
So you close the HIC Valve, (manually) and set the idle with the engine warmed up, You will know for sure the curb idle is correct (if the HIC Valve is operating properly) that it will ONLY ADD extra air to the carb/Intake/Engine under a High Thermal Condition and cause the cooling system to be more efficient due to a higher engine rpm.
Barry Grant claimed to have invented the Idle Air By-pass System "Idle EZE" for carbs but Pontiac had a By-pass idle circuit built into the Rochester 2 BBL Carbs, HIC VALVE, (years before the Barry Grant's claim) on millions of Pontiac engines.
Carter Carbs also had a Idle Air By-Pass Circuit on AFB carbs. It was a manual setting system.
HIC valve is thermally controlled.
Hope that makes sense.
Tom V.
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"Engineers do stuff for reasons" Tom Vaught
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